“…If you created an object in another domain e.g. with AppDomain.CreateInstanceAndUnwrap, all you need to call the object in another domain is to call an object’s method. The simplest way to make a cross-application domain call is just to make a call directly on that object, which actually is exposed from another domain via its proxy, existing in another domain.”
(http://stackoverflow.com/questions/6242573/simplest-way-to-make-cross-appdomain-call)